Highfields Amateur Radio Club
Glossary of Radio Terms.

Appendix:
Battery Details.

Both the PX1 (LR50) and the SR850 are generally deemed to be interchangeable, any difference comes down to equipment fitment. I have noted the differences here for you to decide.

If you need an exact voltage replacement for the discontinued Mercury MR50 producing exactly 1.35 volts, then consider the MR-50 Adapter, Voltage Reducing Converter from the Small Battery Company.
Possibly the best solution for the discontinued MR50, it has the outer dimensions of the MR50 Mercury cell with a recess that takes the inexpensive and easily obtained Silver Oxide 357 cell. Within the adapter are micro electronics that drop the voltage from the 1.55 volts produced by the Silver Oxide cell to the 1.35 volts that your device was designed for. No adjustment or modification to your equipment required. MR-50 Adapters are a one time purchase, and will last a lifetime. Simply replace the expired Silver Oxide 357 cell with a fresh one when required.

Equivalents:

Image not to scale.	Common Name.	Dimensions. Length × Diameter.	Chemical Composition.	Nominal Voltage.
Detail of SR850	PX1.	15.6 mm × 15.6 mm SR850 16.5 mm × 15.7 mm Contacts: Case and flat base Positive Slightly raised area Negitive. The SR850 has one end half of the case Positive and the other end half Negitive (see detail picture).	Alkaline Silver Oxide (Ag2O).	1.5 volts, 1.55 volts (Ag2O) (1.35 volts for the discontinued mercury types)